Method and apparatus for playing back recorded video

ABSTRACT

A method and an apparatus for playing back recorded video from a temporal position within a temporal range of the recorded video is disclosed. The recorded video including intra frames and inter frames and the recorded video including video sequences having different frame rates. The method comprises receiving a request for playing back the recorded video from a specific temporal position recorded in the recorded video, identifying an intra frame at an earlier temporal position in the recorded video than the specific temporal position received in the request, playing back the recorded video in a first mode from the identified intra frame, and playing back the recorded video in a second mode from the specific temporal position in the recorded video when the playing back of the recorded video in the first mode have arrived at the specific temporal position of in the recorded video.

FIELD OF INVENTION

The invention relates to a method and an apparatus for playing backrecorded video from a randomly selected position in the recorded video.The recorded video being recorded using variable frame rate, alsoreferred to as dynamic or variable fps (frames per second).

BACKGROUND

Digital video is the most common and a very popular form in which videosare recorded today. One drawback of digital video is that it requirelarge amounts of storage space on hard drives and a lot of bandwidth inthe networks. This is particularly the case for surveillance video inwhich a lot of video is recorded during vast time frames. In connectionwith the present disclosure, digital video refers to digital motionvideo which uses much more data than digital still images. In order todecrease the amount of data needed to represent a digital video, plentyof compression schemes have been developed, e.g. H.262, H.264, H.265,and MPEG. However, decreasing the amount of data used for representingdigital video is subject to continuously ongoing research.

Video recordings and video streams, compressed or uncompressed, arerepresented by sequences of image frames which are recorded and playedback a specified frequency. This frequency is often referred to as framerate or fps (frames per second). One development in the area of digitalmotion video compression has been to introduce variable frame rate.Variable frame rate is to be understood as the frame rate for a digitalvideo being varied during the duration of the recorded video. Forexample, during a time period with very little movement and/or action inthe scene, e.g. small changes in captured images, the frame rate may beadjusted to a very low value, e.g. 1 fps, and then when the cameraidentifies movement and/or action in the scene, e.g. large or rapidchanges in captured images, the frame rate may be adjusted to a valuefor capturing of the movement, e.g. 30 fps. Hence, variable frame ratepotentially saves a lot of bandwidth and/or storage space. In particularin monitoring or surveillance type scenarios where a lot of recordingsto not include any movement at all.

Common encoding schemes such as MPEG encoding of various types, H.264,H.265, etc. employs an encoding scheme in which some frames arespatially encoded, i.e. encoded based on information in the frameitself, and other frames are temporally encoded, i.e. encoded based onchanges in image elements or objects in relation to a previous imageframe or frames and/or a later image frame or frames. Spatially encodedimage frames are referred to as intra frames and temporally encodedimage frames are referred to as inter frames. Many of the encodingschemes refers to the intra frames as I-frames and refers to the interframes as P- or B-frames. P-frames are related to a previous frame, i.e.in order to be decoded it rely on information of a previously decodedimage frame. B-frames are related to both a previous frame and a futureframe. An image stream or an image file may be described as a sequenceof intra frames and inter frames. Hereinafter will both image streamstreamed to a device and a video file stored and distributed from astorage device may be referred to as an image stream. The image streamhas to start with an intra frame in order to have a complete image whichthe inter frames can depend on. The intra frame is then followed by oneor a plurality of inter frames until another intra frame is present inthe image stream. One intra frame and the following inter frames, whichare preceding the next intra frame, is referred to as a GOP (Group ofPictures). Hence the structure may be depicted like in the two differentstructural examples shown below (I=Intra frames P&B=Inter frames):

-   -   IPPPPBPPPPIPPPPBPPPPIPPPPBPPPPIPPPPBPPPP . . .    -   IPPPPPPPPPPPPPPPPPPIPPPPPPPPPPPPPPPPPP . . .

Another development in this area has been to introduce a techniquecalled variable GOP-length (Group of Pictures). The GOP-length isdefined as one intra frame added to the number of inter frames until thenext intra frame, in the examples above the GOP-length is 10 and 19,respectively. Usually one of the intra frames is included in theGOP-length. The basic idea behind variable GOP-length is based on thefact that an intra-frame requires a lot more data than an inter-frameand that the required storage space or bandwidth will be substantiallyreduced if the intra frames are less frequent, i.e. longer GOP-length.However, there is a drawback with longer GOP-lengths. The drawback isthat the greater number of inter-frames the more artefacts areintroduced in the video due to the inter-frames relying on informationaggregated from previous inter-frames and, thus, artefacts in theseprevious inter-frames are also aggregated. One of the objects of theintra-frame is to reset these artefacts by providing a non-dependentimage frame including the entire image frame. Similar to the use ofvariable frame rate the long GOP-length may be used during periods oflow or no action in order to save storage space and/or bandwidth. Then,in order to avoid too much artefacts in the recorded video theGOP-length is shortened when action and/or movement is present in thescene.

When a user or an operator want to access a recorded video at a specifictemporal location, i.e. a specific time in the recording, the playbackfunction should start playing from the specific temporal location.However, often this temporal location is represented by an inter-frameand because an inter-frame relies on earlier frames in order to displaycorrect image information the playback function has to find an earlierintra-frame and then decode all frames in between the intra-frame andthe inter-frame at the specific temporal location. This operation ofstarting a playback function at the random location in a recorded videois sometimes referred to as a trick play. Other common trick playfunctionalities are fast forward and reverse playback. One way ofimplementing trick plays like these is described in the internationalpatent application WO00/22820. In this application the random access ofa specified temporal location is implemented so that the process afteridentifying the selected frame finds the I-frame, which in this casecorresponds to the previously discussed intra-frame, using informationstored in an auxiliary file including an offset of the I-frame. When theI-frame has been found the I-frame and subsequent P-frames, which inthis case corresponds to the previously discussed inter-frames, will bedecoded but not displayed until the selected frame is decoded. Anotherway of implementing the trick play such as random access to a time pointin video recording is described in the international application WO97/30544. In this application the target frame at the specified timepoint in the recorded video is identified using a video frame indexbeing an array of offset numbers indicating at what byte each picturestarts and whether the picture is an I-, P- or B-frame. Then the earlierframes that the requested frame is depending on is parsed.

These methods are complicated and requires a lot of changes to a basicplayback function not already implementing a random access playbackfunction.

SUMMARY

A method and apparatus to facilitate monitoring and viewing recordedvideo is disclosed. The method and apparatus also facilitates access andinterpretation of recorded surveillance video.

An embodiment of a method for playing back recorded video is describedin claim 1. Further embodiments are presented in the dependent claims.

More specifically, according to one embodiment, a method for playingback recorded video from a temporal position within a temporal range ofthe recorded video, the recorded video including intra frames and interframes, and the recorded video including video sequences havingdifferent frame rates, the method comprises receiving a request forplaying back the recorded video from a specific temporal positionrecorded in the recorded video, identifying an intra frame at an earliertemporal position in the recorded video than the specific temporalposition received in the request, playing back the recorded video in afirst mode from the identified intra frame, and playing back therecorded video in a second mode from the specific temporal position inthe recorded video when the playing back of the recorded video in thefirst mode have arrived at the specific temporal position of in therecorded video. The playing back of the recorded video in the first modeincludes playing back the recorded video at a constant and predeterminedframe rate and in the second mode play back the recorded video at avariable frame rate that is continuously proportional to the frame rateused during recording of corresponding video frame. One advantage of theabove embodiment is that the operator will get a quick overview of amonitored scene leading up to the specified time and still enable toavoid the need of waiting for a long time for the video following therequested time point. Moreover, the switching between the two playbackmodes, i.e. the constant frame rate mode and the variable frame ratemode, allows the method and apparatus described herein to be implementedin both new and existing playback devices.

The temporal position included in the request for playing back therecorded video from a specific temporal position may be entered as atimecode by a user. Alternatively, or additionally, the temporalposition included in the request for playing back the recorded videofrom a specific temporal position may be entered by means of selectingin a graphically presented timeline a specific point in time and/or bymeans of selecting a jump back button representing a predeterminedlength for a jump back in time.

In one embodiment the act of identifying an intra frame includesidentifying an intra frame at a predetermined number of intra framepositions from the specific temporal position. Alternatively the act ofidentifying an intra frame includes identifying the intra frametemporally positioned immediately before the frame at the specifictemporal position.

Moreover, the constant and predetermined frame rate may be set in thedevice playing back the recorded video. In some embodiments the constantand predetermined frame rate is not determined from data in the recordedvideo.

In some embodiments the variable frame rate for the second mode playingback of recorded video is continuously retrieved from frame rate dataincluded in the recorded video data.

According to some embodiments the playing back in the second modeachieves variable frame rate by reading timestamps relating to frames inthe recorded video stream and basing the playing back on thesetimestamps.

Further, the playing back of recorded video may include rendering avideo signal for displaying from the recorded video.

According to another aspect, an apparatus implementing the methoddiscussed above is disclosed.

A further scope of applicability of the present disclosure will becomeapparent from the detailed description given below. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments, are given by way of illustration only,since various changes and modifications within the scope of thedisclosure will become apparent to those skilled in the art from thisdetailed description. Hence, it is to be understood that this disclosureis not limited to the particular component parts of the device describedor steps of the methods described as such device and method may vary. Itis also to be understood that the terminology used herein is for purposeof describing particular embodiments only, and is not intended to belimiting. It must be noted that, as used in the specification and theappended claim, the articles “a,” “an,” “the,” and “said” are intendedto mean that there are one or more of the elements unless the contextclearly dictates otherwise. Thus, for example, reference to “a sensor”or “the sensor” may include several sensors, and the like. Furthermore,the word “comprising” does not exclude other elements or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswhere:

FIG. 1 is schematic block diagram of a system in which an embodiment maybe included;

FIG. 2 is a schematic flowchart of a method according to one embodiment;

FIG. 3a is a schematic view of intra and inter frames in a recordedvideo;

FIG. 3b is a schematic view of intra and inter frames in anotherrecorded video;

FIG. 4a is a schematic view of GOPs in a recorded video corresponding tothe recorded video of FIG. 3 a;

FIG. 4b is a schematic view of GOPs in a recorded video corresponding tothe recorded video of FIG. 3 b;

FIG. 5a is a schematic view of GOPs in a portion of a video recordedusing variable frame rate; and

FIG. 5b is a schematic view of intra and inter frames in the videoshowed in FIG. 5 a.

Further, in the figures like reference characters designate like orcorresponding parts throughout the several figures.

DETAILED DESCRIPTION

A method for random access of temporal locations, i.e. time points, in arecorded video will now be described more fully hereinafter. Therecorded video may be any type of recorded video. However, the method isparticularly suitable for video recordings from monitoring operations orsurveillance operations.

Now referring to FIG. 1 showing a possible system in which a playbackdevice 10 is running a playback method. Playback device may be connectedto a computer network 12 and be connected to a storage device 14. Theplayback device 10 may be a general purpose computer running the videoplayback software operating in accordance with the disclosure, may be adevice that is an integral part in a monitoring/surveillance network forthe purpose of enabling monitoring of video cameras 16 and replay ofrecorded material, may be a device running a video management softwaredesigned for surveillance, etc. The computer network 12 may be any typeof network allowing transfer of video recordings between storage devices14 and a playback device 10, e.g. a Local Area Network (LAN), a WideArea Network (WAN), or the Internet. The storage device 14 of the systemmay be a video server, a media server, a file server, a networkedattached storage (NAS), a network share, a monitoring camera or asurveillance camera storing recordings, etc. Alternatively, the videorecordings for playback may be stored in the playback device itself.

A playback method according to an embodiment includes, see FIG. 2,receiving an input from an operator or user requesting playback of aspecific video recording from a specific point in time in the videorecording, step 102. The operator or user may input a specific point intime by entering a timecode, by selecting a point on the timeline, byselecting the time from a list, by selecting predetermined jump backperiod indicated in the graphical interface, e.g. by means of a boxdisplaying the jump back period. The recording identification mayrepresent the presently viewed live view or another recording selectedby the operator. Then the playback mode is set to constant frame ratemode, step 104, in which mode the play back device is arranged to playback the video at a constant and predetermined frame rate. The framerate may be set before the playback from the specific time point in therecorded video was requested and may for instance be set to normalrecording/playback frame rate such as 30 fps or 25 fps. However thepre-set frame rate may be any frame rate.

The requested video recording is accessed, step 106, at a storage devicein the playback device, a server, a NAS, from a storage deviceincorporated in a camera, etc. Then the requested temporal position inthe recorded video is found by means of reading time stamps stored inthe video recording or stored in connection with the video recording.The time stamps may be stored in connection with each frame in therecorded video or they may be stored in information in a containerformat including the recorded video. An example of such a containerformat is Matroska. These timestamps are also the timestamps used in asecond playback mode referred to as variable frame rate mode and whichis used when the playback should be representing a normal playbackspeed, i.e. the events recorded is played back at a “real time” speed ora natural speed which corresponds to the speed at which the event wasrecorded. When the correct temporal position is found in the videorecording an intra frame that is earlier in the video stream may befound by looking at a frame to which the frame at the temporal positionis related for decoding and by checking if that frame is an intra frameor not. If it is an intra frame then the intra frame has been foundotherwise the process have to proceed and look at a frame related tothis latest checked inter frame for decoding. This type of backtracking, i.e. checking a temporally earlier frame, is then performeduntil the intra frame is found. Multiple intra frame back tracking maybe achieved in the same way with the addition of counting the number ofintra frames identified. Hence an intra frame to start decoding andplayback from is found by parsing back in time until the desired numberof intra frames have been identified, step 108, and wherein in someembodiments the first intra frame identified is the intra frame to startdecoding and playback from. In some applications it is most interestingto start from the first intra frame preceding the requested temporalposition in the video recording, i.e. the intra frame belonging the sameGOP as the frame at the requested temporal position. However, in otherapplications it may be interesting to start the playback from evenearlier intra frames by simply counting a predetermined number of intraframes when parsing for earlier intra frames and then start to play backat the desired intra frame when this desired intra frame is located.When the intra frame is found the playback of the recorded video isstarted from this intra frame using the current playback mode, which isthe constant frame rate mode, step 110. From the start of the playbackthe frames to be displayed are checked in order to determine if theframe is a frame corresponding to the requested temporal position forthe playback, step 112. If the requested temporal position has not beenreached the playback continues playing back the next frame at thecurrent playback mode, which still will be the constant frame rate mode,step 114. Then, the process returns to step 112 in order to check if therequested temporal position has been reached yet. When, the requestedtemporal position has been reached the process proceed to step 116 andswitches the playback mode to variable frame rate mode and then theplaying back of the next frame in step 114 will be in the variable framerate mode. The playback will continue to playback the recorded video inthe variable frame rate mode until the playback is stopped or anothertrick play is requested.

As mentioned above, the recorded video played back using the disclosedembodiments is recorded implementing variable frame rate. In FIGS. 3aand 3b two video recordings both having constant frame rates butdifferent frame rates are shown over a time period of little more thantwo seconds. Each intra frame is depicted as a short line with a circleon top and each inter frame is depicted as a short line. In FIG. 3a theGOP-length is 30 frames and the frame rate is 30 fps, as one GOP-lengthof 30 frames represents one second of video. In FIG. 3b the GOP-lengthis still 30 frames, but the time period represented by these 30 framesis two seconds instead of one. Hence, the frame rate of FIG. 3b is 15fps. If the recorded video of FIGS. 3a and 3b are played back at thesame frame rate, let us say 30 fps, then the video recording of FIG. 3awould be played back at real time speed, i.e. the speed it was recordedat. However, the recorded video of FIG. 3b would be played back at twotimes the speed, i.e. fast forwarded by two times, as the 30 framesrepresenting 2 seconds of recorded material is played back in onesecond.

In FIGS. 4a-4b a longer sequence of each of the two video recordings ofFIGS. 3a-3b is shown. Each square represents a GOP of 30 frames and asboth recordings have the same GOP-length but different frame rate.Accordingly, one obvious difference between the two video recordings ofFIGS. 4a-4b is that in the video recording of FIG. 4a 60 seconds isrepresented by 60 GOPs, i.e. 60×30=1800 frames, and in the videorecording of FIG. 4b 60 seconds is represented by 30 GOP, 30×30=900frames.

Now referring to FIGS. 5a-5b in which a change of frame rates in avariable framerate video recording is shown. In this example the GOPlengths are still kept constant and is set to 30 frames as in theprevious examples of constant frame rate recordings in FIGS. 3a, 3b, 4aand 4b . The first 60 seconds is represented by a single GOP andaccordingly the frame rate during these 60 seconds is 0.5 fps. Then, at60 seconds the frame rate becomes higher, in this case 30 fps. Thereason for the higher frame rate may be that movement has been detectedduring recording and the system is arranged to capture such events at ahigher frame rate. Other, reasons for the higher frame rate may be thatan input to the camera from, for example, an alarm system, an externalmotion detector, a door opening sensor, a window opening sensor, a lightsensor, etc. is received and trigger the higher frame rate. There may beplenty of events and/or reasons for a higher frame rate. However, therecording of the video is not part of the present disclosure and willtherefore not be described in more detail.

In one possible scenario an operator or user selects, in any waydescribed earlier, a random temporal position in the recorded video,indicated by arrow 150. The frame at the temporal position is an interframe which is depending on earlier frames in order to be decodedproperly. In a prior art system the playback device then will search andfind an intra frame that is earlier than the inter frame at the selectedtemporal position and start playback from the intra frame. The systemwill then play back non requested video frames, but this would not be aproblem in most systems because the playback will show these extraframes quite quickly due to the fps being relatively high and theGOP-length being moderate. Hence, these extra frames that are playedback will hardly be noticed by the operator because the high fps willmake them be showed in a second or at least during a short time period.However, when variable frame rate is implemented as in FIGS. 5a-5b therecorded video is played back in at real time frame rates, i.e. theframe rate used when recording each specific frame, therefore thewaiting time for arriving at the requested temporal position when theplayback device is playing back all frames from the earlier intra framemay be long. In the example of FIGS. 5a-5b the waiting time will bealmost one minute and the setup could even result in worse waiting timeif the GOP-length is longer and/or the fps is even lower.

In one embodiment, this scenario will be processed differently than inthe prior art. The system will still search for the earlier intra frameand start playback from that intra frame. However, the play back isperformed in a constant frame rate mode MODE 1. Hence, the system simplyoverrides the variable frame rate setting and play back at a constantframe rate. Then, when the frame at the requested temporal position isto be played back, the system switches playback mode from constant framerate mode MODE 1 to variable frame rate mode MODE 2 and thereby switchesinto playing back the video recording from the requested temporalposition in e.g. real time. Let us assume that the constant frame rateis set to 30 fps, then in the example of FIGS. 5a-5b the playback duringMODE 1 will take less than a second, i.e. playing back 26 frames at 30fps. At the requested temporal position 150 the playback mode isswitched to the variable frame rate mode MODE 2 resulting in that theframes from the requested temporal position 150 to the 60 secondsposition in the figure will take four seconds to play back.

The change of frame rate in a video recording is not bound to change atthe start of a new GOP, but may change in the middle of a GOP. Hence, incase of an interesting temporal position is interesting due to movementin the captured scene, then the frame rate will be increased when themovement is detected as the recording system increases the recordingframe rate when the captured scene includes movement. If this increasedframe rate is at the end of a GOP then the prior art play back schemewill have to play back from the intra frame at a slow frame rate untilthe interesting high frame rate section of the GOP is reached andthereby wasting a lot of time for the operator. The implementationaccording to the disclosed embodiments will quickly show the low framerate frames, as it will play them back at constant frame rate instead ofin real time, thereby presenting a quick view of the scene before therequested temporal position and then switch to real time at therequested temporal position.

Playback in constant frame rate mode may be implemented as any standardplayback method in which the frame rate is set to a predetermined value.This is a common way of implementing playback functions in playbackdevices and it includes initially reading a value indicating the framerate, i.e. the fps of the recorded video, and then decoding andrendering an image to display from the encoded recorded video at thefrequency initially set by the predetermined frame rate. Playback atvariable frame rate mode are, as previously mentioned, a playback methodplaying back recorded variable frame rate video at a speed proportionalto the real time speed at the capturing of the video. Accordingly, thismode will play back the recorded video at a rate that makes the videoplay back show moving objects moving at the same speed as they did atthe capturing of the video or if slow motion or fast forward is selectedat a speed that is X times the speed at the capture. Wherein X=2 isinterpreted as a double playback speed in relation to the natural speed.In order to enable this each frame in the motion video recording isprovided with or related to a time stamp reflecting the time of capture.The playback device is then reading the time stamp and makes it displayat the correct time in relation to the previous image frame.

In some examples above a frame rate lower than 1 fps is used. For somedecoders frame rates lower than 1 fps is difficult to manage at a goodquality and in those cases the lowest frame rate should be 1 fps.However, if no such limitation is present in the decoders, then framerates below 1 fps may be used.

What is claimed is:
 1. Method for playing back recorded video from atemporal position within a temporal range of the recorded video, therecorded video including intra frames and inter frames, and the recordedvideo including video sequences having different frame rates, the methodcomprising: receiving a request for playing back the recorded video froma specific temporal position recorded in the recorded video, thespecific temporal position being at an inter frame; identifying an intraframe at an earlier temporal position in the recorded video than thespecific temporal position received in the request; playing back therecorded video in a first mode from the identified intra frame to thespecific temporal position; and playing back the recorded video in asecond mode from the specific temporal position in the recorded videowhen the playing back of the recorded video in the first mode havearrived at the specific temporal position of in the recorded video,wherein playing back recorded video includes rendering a video signalfor displaying from the recorded video, wherein the playing back of therecorded video in the first mode includes playing back the recordedvideo at a constant and predetermined frame rate and in the second modeplay back the recorded video at a variable frame rate that iscontinuously proportional to the frame rate used during recording ofcorresponding video frame, and wherein the constant and predeterminedframe rate is set in the device playing back the recorded video. 2.Method according to claim 1, wherein the temporal position included inthe request for playing back the recorded video from a specific temporalposition is entered as a timecode by a user.
 3. Method according toclaim 1, wherein the temporal position included in the request forplaying back the recorded video from a specific temporal position isentered by selecting in a graphically presented timeline a specificpoint in time.
 4. Method according to claim 1, wherein the temporalposition included in the request for playing back the recorded videofrom a specific temporal position is entered by selecting a jump backbutton representing a predetermined length for a jump back in time. 5.Method according to claim 1, wherein identifying an intra frame includesidentifying an intra frame at a predetermined number of intra framepositions from the specific temporal position.
 6. Method according toclaim 1, wherein identifying an intra frame includes identifying theintra frame temporally positioned immediately before the frame at thespecific temporal position.
 7. Method according to claim 1, wherein theconstant and predetermined frame rate is set in a device playing backthe recorded video.
 8. Method according to claim 1, wherein the constantand predetermined frame rate is not determined from data in the recordedvideo.
 9. Method according to claim 1, wherein the variable frame ratefor the second mode playing back of recorded video is continuouslyretrieved from frame rate data included in data in the recorded video.10. Method according to claim 1, wherein the playing back in the secondmode achieves variable frame rate by reading timestamps relating toframes in the recorded video and basing the playing back of the recordedvideo on these timestamps.
 11. Apparatus configured to play backrecorded video from a temporal position within a temporal range of therecorded video, the recorded video including intra frames and interframes, and the recorded video including video sequences havingdifferent frame rates, the apparatus comprises: a receiving deviceconfigured to receive a request for playing back the recorded video froma specific temporal position recorded in the recorded video, thespecific temporal position being at an inter frame; an identifyingdevice configured to identify an intra frame at an earlier temporalposition in the recorded video than the specific temporal positionreceived in the request; and a playback device configured to play backthe recorded video in a first mode from the identified intra frame tothe specific temporal position and to play back the recorded video in asecond mode from the specific temporal position in the recorded videowhen the playing back of the recorded video in the first mode havearrived at the specific temporal position of in the recorded video,wherein the playback device is configured to play back recorded video byperforming operations including rendering a video signal for displayingfrom the recorded video, and wherein the playback device is configuredto play back of the recorded video in the first mode by performingoperations including playing back the recorded video at a constant andpredetermined frame rate and the playback device is configured to playback the recorded video in the second mode at a variable frame rate thatis continuously proportional to the frame rate used during recording ofcorresponding video frames, wherein the constant and predetermined framerate is set in the device playing back the recorded video.
 12. Apparatusaccording to claim 11, wherein the temporal position included in therequest for playing back the recorded video from a specific temporalposition include a timecode.
 13. Apparatus according to claim 11,wherein the temporal position included in the request for playing backthe recorded video from a specific temporal position is entered by meansof selecting in a graphically presented timeline a specific point intime.
 14. Apparatus according to claim 11, wherein the temporal positionincluded in the request for playing back the recorded video from aspecific temporal position is entered by means of selecting a jump backbutton representing a predetermined length for a jump back in time. 15.Apparatus according to claim 11, wherein identifying an intra frameincludes identifying an intra frame at a predetermined number of intraframe positions from the specific temporal position.
 16. Apparatusaccording to claim 11, wherein identifying an intra frame includesidentifying the intra frame temporally positioned immediately before theframe at the specific temporal position.
 17. Apparatus according toclaim 11, wherein the constant and predetermined frame rate is set inthe device playing back the recorded video.
 18. Apparatus according toclaim 11, wherein the constant and predetermined frame rate is notdetermined from data in the recorded video.
 19. Apparatus according toclaim 11, wherein the variable frame rate for the second mode playingback of recorded video is continuously retrieved from frame rate dataincluded in data in the recorded video.
 20. Apparatus according to claim11, wherein the playing back in the second mode achieves variable framerate by reading timestamps relating to frames in the recorded video andbasing the playing back of the recorded video on these timestamps.